package likouJava;

import java.util.HashMap;

public class 最长回文子串 {
    public String longestPalindrome(String s) {
        if(s == null || s.length() < 1){
            return "";
        }
        int start = 0;
        int end = 0;
        for (int i = 0; i < s.length(); i++) {
            int len1 = expandCenter(s,i,i);
            int len2 = expandCenter(s,i,i+1);
            int len = Math.max(len1,len2);
            if(len > end - start){
                start = i - (len - 1) / 2;
                end = i +len / 2;
            }
        }
        return s.substring(start,end+1);
    }

    private int expandCenter(String s,int left ,int right){
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)){
            left--;
            right++;
        }
        return right - left -1;
    }

}
